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Written by Chris Mulcahy
RC Helicopters
Column
As seen in the July 2018 issue of
Model Aviation.





The R5 looks fast in a hover. Its fuselage is bright and easy to see.


One aspect of the hobby that I have never tried is building and flying a dedicated speed helicopter. There aren’t many purpose-built speed machines to choose from, but we certainly have a few more than we used to.

During the winter, I had a chance to start on my own speed machine, the Gaui R5. At first glance, the R5 has a stunning appearance. It is extremely slim, with a full-body fuselage and no visible signs of any landing gear. It just looks fast.

When you lift the hood, you start to get a glimpse of the passion and creativity that went into cramming a 700-size powerplant into a 550-size helicopter.

The kit came with Halo 550 mm main and 80 mm tail blades. Although I used the tail blades, I decided to use Rail Blades 626 main blades at the recommendation of other R5 owners.

The kit is made of aluminum and carbon fiber. The fuselage is prepainted fiberglass with carbon-fiber reinforcements and a bright, glossy finish. It came with a printed instruction manual and the screws, nuts, and bolts were grouped together in labeled bags. This made it easy to find each bolt needed during the build.




The beginning of the build. Everything was packaged well!


The build went smoothly, and I was impressed with the quality of the parts. Tolerances were perfect, finishes were immaculate, and every part went together smoothly and accurately. It was a joy to build.

There were a few subassemblies that I took apart to apply threadlocker. Sometimes parts are put together at the factory during packaging to ensure that everything is included.

The R5 features a belt and pulley system to drive the rotorhead. The motor is connected to a pulley, which in turn meshes into the main gear (see my June 2018 column about gear ratios).

To carry all of that power, Gaui made the main gear taller than most. The tail is also belt driven, with a cool sprung tensioner on the side. The tail servo drives a bellcrank, which then drives the tail rotor pushrod. It is a smooth operation.

The tail rotor hub is a beautiful piece of aluminum, made from a single piece with merely a small cap to complete the assembly. There is ample room up front for any type of ESC. I chose to install a Castle Creations Edge HV 160.

I installed a Scorpion HKII-4235-630KV LE motor, Futaba CGY750 gyro, Futaba BLS272/274 cyclic/tail servos, and a Futaba R7008SB receiver guided by my Futaba 16SZ transmitter. I made a 12S stick pack from two Pulse 6S 3,700 mAh LiPo batteries and used a 2S 2,250 mAh receiver pack. The R5 has a removeable battery tray that slides in easily, with a good, solid retaining latch. I had to cut the motor shaft because it was too long and intruded into the battery area.

But wait. What about that landing gear? The R5 uses a unique rotating bar at the base of its fuselage. When deployed, it sits perpendicular to the longitudinal axis of the helicopter (it sticks out sideways). When in flight, it rotates 90° and becomes flush with the fuselage, practically disappearing. Gaui includes a small servo with a voltage regulator to drive the landing gear.




The video shows the landing skid rotation in action.





The landing skid is deployed and the R5 is ready to land.


One thing that I learned during the build was to plan out my electronics installation before putting it into the rear half of the fuselage. I spent some time exploring mounting options for my receiver and gyro before permanently attaching them and tidying up all of the wiring.

After this was complete, I slid the mechanics into the fuselage and finished attaching the tail hub. Using Castle Creations Castle Link programming software, I programmed the ESC so that I had three head speeds to experiment with: 2,280 rpm, 2,510 rpm, and 3,018 rpm. The gyro was set up as stock, although I later decreased the tail gyro gain quite a bit.




The beginning of the build. Everything was packaged well!



Flying

I admit that I was nervous about flying it for the first time—not so much the flying as engaging the “ludicrous speed” of 3,000 rpm! I had never set up a speed helicopter, so I set it up in the same way as I do my 3D helicopters using a linear pitch curve.

The only difference was that I set it up with 14° of pitch. I also decided to run approximately 35% exponential on the elevator and aileron channels to help keep things smooth at high speed. I was unsure how the landing gear would behave because the machine is so narrow.

As it was spooling up for the first time, I gave it a little positive pitch to keep it light on the skid and to prevent the tail fin from sticking into the ground. This seemed to be key because lifting off was uneventful. Right away, the helicopter was smooth.

I flew a few figure eights and spent some time dialing down the tail gain. Each of the higher head speeds required less tail gain than the previous head speed.

A few more passes and I clicked up to 2,280 rpm. I did another pass or two and then increased to 3,018 rpm! The helicopter made a unique sound and reminded me of what I had heard at the International Radio Controlled Helicopter Association (IRCHA) Speed Cup contest in previous years.

Model Aviation Magazine - RC Helicopters July 2018

I flew by and pulled straight up. The aircraft continued vertical more than any of my 3D helicopters have done. It just kept coasting up!

I did a 180° pirouette/hammerhead and pushed in as much pitch as I dared. The R5 came screaming by at a speed at which I had never flown a helicopter. It was fast! I repeated my turnaround maneuver and the run, this time with a tailwind, and it went screaming by even faster than before. It was straight as an arrow and practically flew itself.

I had my timer set to 3 minutes and decided to land. After bringing the R5 to a standstill, I deployed the landing gear, hovered down to approximately a foot above the ground, and hit throttlehold. As the head speed bled off, I gently set it down on the field. After several flights, I didn’t have any issues with the landing gear, but it seemed to be a good idea to use a gentle touch on landing.

By the way, the R5 is capable of aerobatics too. I wouldn’t do any hard 3D with it, but you can certainly loop it, roll it, fly upside down, and even perform pirouetting flips if you feel so inclined. I enjoy this helicopter and can’t wait to see what it can really do when I have more experience with it!




The author after a successful maiden flight.



Bonus Photos

Model Aviation Magazine - RC Helicopters July 2018



Sources:

Gaui
gaui@gaui.com.tw
www.gaui.com.tw

Futaba
www.futabarc.com

Castle Creations
(913) 390-6939
www.castlecreations.com

Scorpion Power System
support@spihk.com
www.scorpionsystem.com

Pulse Battery
(978) 206-6037
www.pulsebattery.com

IRCHA
www.ircha.org

Gaui R5 Maiden Day
www.youtube.com/watch?v=ohTvo3JWDw0






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